Nacelle assembly for a gas turbine engine

ABSTRACT

A nacelle assembly  40  adapted for mounting on a ducted fan gas turbine engine  20  comprising a generally annular body  46  having an air inlet  42  and an air outlet  44 , the generally annular body  46  encircling a region of the engine  20  when working in operative association with the engine  20  and has a first attachment means  48  to a rigid member  58  and a second attachment means  52  to a casing assembly  34  on the engine  20  wherein the second attachment means  52  is frangible.

The present invention relates to a ducted gas turbine engine andincludes a nacelle assembly which is detachably connected to a ductedgas turbine engine.

Ducted gas turbine engines usually comprise a core engine which drives apropulsive fan assembly. The fan assembly comprises a number of radiallyextending aerofoil blades mounted on a common hub and enclosed within agenerally cylindrical casing assembly. The fan assembly and casingassembly are encircled by a generally annular nacelle assembly whichforms the air intake of the engine and is aerodynamically shaped. Thenacelle may extend both forward and rearward, relative to the directionof airflow, of the fan assembly.

There is a remote possibility with such engines that part or all of oneor more of the fan blades could become detached from the remainder ofthe fan assembly. The occurrence of a part or all of one or more of thefan blades becoming detached from the fan assembly and impacting thecasing assembly is hereinafter termed a FBO (fan blade off) event. Thecasing assembly surrounding the fan assembly is specifically designed tocontain the detached blade or blade portion. However, it is importantthat the nacelle is not damaged during the FBO event as the casingassembly is subject to distortion. It is also important to remove thepossibility of further damage to the nacelle, after the FBO event,resulting from vibrations during run down and subsequent windmilling dueto the fan assembly being out of balance. Run down being hereinafterdefined as the deceleration of axial rotational speed of the engine fromthe rotational speed at which a fan blade or part of a fan blade hasbeen released and caused safety systems to shut down the engine.Windmilling being hereinafter defined as the axial rotation of the fanassembly arising from air ingressing the engine due to the forward speedof the aircraft after engine shut down.

Typically the nacelle assembly may be attached to a component of theengine and/or an engine support pylon assembly with the necessary accessto the engine and engine core mounted accessories usually made by eitheropening fan cowl doors located in the body of the nacelle as describedin WO93/02920 or by the nacelle assembly comprising two part-circularportions acting in a clam-shell like manner as described in U.S. Pat.No. 5,205,513. Furthermore, the nacelle assembly is commonly attached tothe fan casing as described in U.S. Pat. No. 4,044,973, with suchattachments being required to be particularly robust to maintainattachment after a FBO event. The nacelle designs, in particular theattachment means to the engine and/or pylon, of the prior art hereincited lend themselves to complex and heavy, thus expensive, assemblies.The nacelle assemblies also appear to be prone to damage during a FBOevent and subsequent vibrational damage caused by windmilling of the outof balance fan assembly during fly home.

It is an object of the present invention to provide a lightweight andlow cost nacelle assembly, attached to the engine in such a way as to bereleasably detachable therefrom during a FBO event and thereby isolatingthe nacelle assembly from potentially destructive fan assemblyvibrations.

According to the present invention there is provided a nacelle assemblyadapted for mounting on a ducted fan gas turbine engine comprising agenerally annular body having an air inlet and an air outlet, thegenerally annular body encircling a region of the engine when working inoperative association with the engine and has a first attachment meansto a rigid member and a second attachment means to a casing assembly onthe engine wherein the second attachment means is frangible.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the casing assembly comprises a containment casing andsurrounds a fan assembly.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the second attachment means provides support in theradial direction.

Preferably the nacelle assembly is adapted for mounting on a gas turbinewherein the second attachment means detaches the nacelle assembly fromthe casing assembly during a FBO event.

Preferably a nacelle assembly adapted for mounting on a gas turbinewherein the rigid member is a component of the engine. Alternatively thenacelle assembly is adapted for mounting on a gas turbine engine whereinthe rigid member is a component of a pylon structure or an aircraftstructure.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the first attachment means provides support for thenacelle in the radial, axial and circumferential directions.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the first attachment means is a releasable attachment.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the annular body comprises a radially outer facing and aradially inner facing defining a space therebetween.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the annular body comprises the outer facing and innerfacing joining and extending rearward of the space to form a singleskin. Alternatively the nacelle assembly is adapted for mounting on agas turbine engine wherein the outer facing and inner facing areconstructed from sandwich constructions.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the space contains a lightweight core, the lightweightcore attached to both the outer facing and the inner facing.Alternatively the nacelle assembly is adapted for mounting on a gasturbine engine wherein the space contains a connector, the connectorattached to both the outer facing and the inner facing.

Preferably the nacelle assembly is adapted for mounting on a gas turbineengine wherein the connector extends substantially in the axialdirection. Alternatively the nacelle assembly is adapted for mounting ona gas turbine engine wherein the connector extends substantially in thecircumferential direction.

Preferably the nacelle assembly is adapted for mounting on a gas turbinewherein the annular body includes an access panel. Alternatively thenacelle assembly is adapted for mounting on a gas turbine engine whereinan engine accessory is operationally located within the space in theannular body.

Preferably a method for assembling a nacelle assembly with an enginecomprises the steps aligning the nacelle assembly and the enginesubstantially parallel to the engine rotation axis, translating thenacelle assembly along the axis to engage the first and secondattachments, and securing the first attachment.

Preferably a method for removing a nacelle assembly from an enginecomprises the steps releasing the first attachment, translating thenacelle assembly substantially parallel to the axis of the engine.

A specific embodiment of the invention will now be described by way ofexample with reference to the accompanying drawing in which:

FIG. 1 is a schematic axial cross section side view of a ducted gasturbine engine in accordance with the present invention.

FIG. 2 is a schematic axial cross section side view of the front portionof a ducted gas turbine engine in accordance with the present invention.

FIG. 3 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 4 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 5 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 6 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 6A is a schematic axial cross section side view enlargement of aportion of the embodiment, shown in FIG. 6, of a nacelle bodyconstruction in accordance with the present invention.

FIG. 7 is a schematic cross section side view of another embodiment of anacelle body construction in accordance with the present invention.

FIG. 7A is a schematic axial cross section side view as shown on FIG. 7of the embodiment of a nacelle body construction in accordance with thepresent invention.

FIG. 8 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 9 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

FIG. 10 is a schematic axial cross section side view of anotherembodiment of a nacelle body construction in accordance with the presentinvention.

Referring to FIG. 1, a ducted gas turbine engine 20 of known generalconfiguration and method of operation, comprises a rotational axis 21 ofthe engine 20, an engine core 22 surrounded by a core casing 24 andwhich drives a propulsive fan assembly 26. The fan assembly 26 comprisesa retention disc 28 with an array of radially extending aerofoil blades30. The engine 20 is secured to an aircraft wing (not shown) from theengine core casing 24 by an engine support pylon assembly 32 in knownmanner. Alternatively, the engine 20 may be mounted to the aircraftstructure (not shown) A nacelle assembly 40 encircles a region of theengine 20.

Referring to FIG. 2, a casing assembly 34 surrounding the fan assembly26 and secured to an annular array of radially extending vanes 36comprises a containment casing 38 for retention of a blade 30 or aportion of a blade 30 during a FBO event.

The nacelle assembly 40 comprises an air inlet 42 and an air outlet 44and a generally annular body 46 which encircles a region of the engine20. In particular the nacelle 40 encircles a region of both the casingassembly 34 and the fan assembly 26 and is extended rearwards forattachment by a first attachment means 48 to a strengthening ring 50.The first attachment 48 means is made by conventional means as known inthe art so as to provide axial, radial and circumferential support tothe nacelle assembly 40. The nacelle assembly 40 is also attached at thefront of the casing assembly 34 by a second attachment means 52, thesecond attachment means 52 is a frangible attachment 52 of constructionas known in the art. The second attachment means 52, located upstream ofthe first attachment means 48, provides support in the radial directionassisting alignment of a gas washed inner nacelle surface 54 and acasing assembly inner surface 56. The frangible attachment 52 isdesigned to detach the nacelle 40 and the engine casing assembly 34during a FBO event.

During a FBO event a blade 30 or blade portion 30 is released from thefan assembly 26 and strikes the containment casing 38, part of thecasing assembly 34, causing the containment casing 38 and the casingassembly 34 to distort from their original shape. It is an advantage ofthe present invention that the nacelle 40 detaches from the enginecasing assembly 34 during the FBO event so that the nacelle assembly 40is not damaged. It is another advantage that the nacelle assembly 40 isno longer attached to the casing assembly 34 after the FBO event as itis not subject to the consequential vibrations arising from the out ofbalance of the fan assembly during run down and windmilling.

The strengthening ring 50 is attached to the engine core casing 24 by arigid member 58 as known in the art.

The nacelle assembly 40 also comprises an acoustic lining 60 configuredand implemented as known in the art.

The nacelle assembly 40 also comprises an anti-icing means 62 as knownin the art.

The nacelle assembly 40 is configured to form an annular space 64radially outward of the casing assembly 34 to accommodate an engineaccessory 66. The annular space 64 also provides a space for the casingassembly 34 to deflect without contacting the nacelle assembly 40 duringa FBO event.

The nacelle assembly 40 provides an aerodynamic external profile for theengine 20 and an aerodynamic air inlet 42 and air outlet 44 for thepropulsive fan assembly 26.

The construction of the nacelle assembly 40 and in particular theannular body 46 is intrinsic to the implementation of the invention. Itis intended that the nacelle body 46 is both lightweight and strong. Thefollowing descriptions with reference to FIGS. 3 to 10 give details offurther embodiments of the annular body 46 in accordance with thepresent invention.

During normal operation of an engine 20 the nacelle assembly 40 carriesaerodynamic loads and loads generated from flexural displacements of theengine 20 and/or the pylon assembly 32.

The method for removal of the nacelle assembly 40, particularly foraccess to the engine 20, is by way of releasing the first attachmentmeans 48 and translating the nacelle assembly 40 in a generally forwardaxial direction relative to the engine 20. The second attachment means52 being so arranged as to disengage the nacelle assembly from thecasing assembly 34 when the nacelle assembly 40 is translated forwardwith respect to the engine 20. Similarly, the method for attachment ofthe nacelle assembly 40 to the engine 20 is by way of translating thenacelle assembly 40 in a generally rearward axial direction relative tothe engine 20 thereby engaging the second attachment means 52 and firstattachment means 48. It is preferable for the first attachment means 48to be relatively easy and quick to release, such attachment means may beconventional clamps, “V”-blades or latches.

Other embodiments of the present invention described hereinafterdescribe configurations of the nacelle assembly's 40 annular body 46which perform the aforementioned load carrying. It is important for theannular body 46 to be lightweight and relatively strong particularlyafter a FBO event. The annular body 46 is required to remain intact andoperational throughout the remainder of the flight of the aircraft (notshown). After a FBO event the annular body 46 is attached only by thefirst attachment means 48 and is subject to aerodynamic loads and loadsgenerated from flexural displacements of the engine 20 and/or the pylonassembly 32. The construction of the annular body 46 is thereforerequired to be lightweight and strong and the following embodimentshereafter of the present invention describe such constructions.

In another embodiment of the present invention referring to FIG. 3, theconstruction of the nacelle body 46 is generally annular with respect tothe rotational axis 21 of the engine 20 and comprises a radially outerfacing 68 and radially inner facing 70. Both the outer facing 68 and theinner facing 70 are relatively thin, strong and stiff and define aninternal space 86 therebetween.

The configuration of the nacelle assembly 46 is designed to form aannular space 64 (FIG. 2) radially outward of the casing assembly 34 toaccommodate engine accessories 66. This is achieved by discontinuing theinternal space 86 in the region of the second attachment means 52 andjoining the outer facing 68 with the inner facing 70 to form a singleskin 74. The single skin 74 extends rearward to the first attachmentmeans 48 at the strengthening ring 50.

In a another embodiment of the present invention referring to FIG. 4,the construction of the nacelle body 46 comprises a relatively thin,strong and stiff radially outer facing 68 and radially inner facing 70generally surrounding a lightweight main core 72 as known in the art asa sandwich construction. The purpose of the main core 66 being totransfer bending shear, torque, compressive and tensile stresses andloads between the outer facing 68 and the inner facing 70.

In another embodiment of the present invention, referring to FIG. 5, anannular body 46 as described with reference to the embodiment shown inFIG. 3 having an access panel 76 located in the single skin 74. Theaccess panel 76 allowing access to the engine accessory 66 withoutremoval of the nacelle assembly 40.

In another embodiment of the present invention, referring to FIG. 6 andFIG. 6A, an annular body 46 as described with reference to theembodiment shown in FIGS. 3, 4 and 5 comprising items that are common toboth, the outer facing 68 and the inner facing 70 are formed fromsandwich constructions themselves with an outer sub-facing 78 and aninner sub-facing 80 generally surrounding a sub-core 82. The outersub-facing 78 relating to an exterior surface 84 of the annular body 46.The embodiment described with reference to FIG. 5 may also comprise aninternal space 86 rather than a main core 72. The embodiment describedwith reference to FIG. 5 may also comprise an access panel 76 asdescribed with reference to FIG. 5.

In another embodiment of the present invention, referring to FIG. 7, anannular body 46 as described with reference to the embodiments shown inFIGS. 3, 5, 6, 6A comprising an annular array of webs 88 connecting theouter facing 68 and the inner facing 70. Each web 88 extends axially tothereby define an array of voids 90 (FIG. 7A). The webs 88 may extendfor the entire axial distance of the void 90 (FIG. 7A) or may extend fora portion of the axial distance of the void 90, so that the voids 90 areinterconnected with each other.

In another embodiment of the present invention, referring to FIG. 8, anannular body 46 as described with reference to the embodiments shown inFIGS. 3, 5, 6, 6A comprising a substantially annular connector 92connecting the outer facing 68 and the inner facing 70. The connector 92extends substantially radially between the outer facing 68 and the innerfacing 70.

In another embodiment of the present invention, referring to FIG. 9, anannular body 46 as described with reference to the embodiments shown inFIGS. 3, 4, 5, 6, 6A, 7, 7A, 8 comprising extending the internal space86 rearward in the annular body 46. For this embodiment it is intendedfor the internal space to be extended to the region of the firstattachment means 48. The internal space 86 may also comprise a main core72 or any of the features such as the web 90 or the connector 92.

In another embodiment of the present invention, referring to FIG. 10, anannular body 46 as described with reference to the embodiments shown inFIGS. 3, 4, 5, 6, 6A, 7, 7A, 8, 9 comprising arranging the engineaccessory 66 between the outer facing 68 and inner facing 70 of theannular body 46. With reference to the aforesaid embodiments the engineaccessory 66 may be positioned substantially within the internal space86, the void 92 or the annular void 94.

Although the present invention has been described with reference to thefirst attachment means 48 being releasably attached to the strengtheningring 50 the first attachment means 48 may also be attached in a similarmanner to any relatively rigid engine 20 component, such as the casingassembly 34, the annular array of vanes 36 or the rigid member 58.

Suitable materials for the facing 68, 70, 78, 80 and single skin 74,access panel 76 and the web 88 and the connector 92 includethermoplastics and thermosets (eg. polythene, polycarbonate,polyethersulphone, polyetheretherketone (PEEK), polyvinylchloride (PVC),epoxy resin cured by amines, nylon, polytetraflouroethelene (PTFE)),resins (e.g. Epoxy, polyamides, phenolic, silicone, cyanoacrylates,anaerobics and acrylics), ceramics (e.g. silicon nitride, siliconcarbide, glass-ceramics), aluminium alloys (e.g. Al—Cu, Al—Mg, AL—Mg—Si,Al—Zn—Mg, Al—Li), magnesium alloys, titanium alloys and nickel, whichmay be reinforced with the following materials: glass, aramid, carbon,alumina, silicon carbide. Suitable materials for the main core 72 andthe sub-core 82 include expanded plastics (e.g. polyurethane), lowdensity woods, honeycomb structures (e.g. aluminium, paper).

I claim:
 1. A nacelle assembly adapted for mounting on a ducted fan gasturbine engine comprising a generally annular body having an air inletand an air outlet, a first attachment means and a second attachmentmeans, the generally annular body encircling a region of the engine whenworking in operative association with the engine, the first attachmentmeans attached to a rigid member and a second attachment means attachedto a casing assembly on the engine wherein the second attachment meansis frangible and detaches the nacelle assembly from the casing assemblyduring a FBO event.
 2. A nacelle assembly adapted for mounting on a gasturbine engine as claimed in claim 1 wherein the casing assemblycomprises a containment casing, the a containment casing surrounds a fanassembly.
 3. A nacelle assembly adapted for mounting on a gas turbineengine as claimed in claim 1 wherein the second attachment meansprovides support in the radial direction.
 4. A nacelle assembly adaptedfor mounting on a gas turbine engine as claimed in claim 1 wherein therigid member is a component of the engine.
 5. A nacelle assembly adaptedfor mounting on a gas turbine engine as claimed in claim 1 wherein therigid member is a pylon assembly structure.
 6. A nacelle assemblyadapted for mounting on a gas turbine engine as claimed in claim 1wherein the rigid member is a component of the aircraft structure.
 7. Anacelle assembly adapted for mounting on a gas turbine engine as claimedin claim 1 wherein the first attachment means provides support for thenacelle in the radial, axial and circumferential directions.
 8. Anacelle assembly adapted for mounting on a gas turbine engine as claimedin claim 1 wherein the first attachment means is a releasableattachment.
 9. A nacelle assembly adapted for mounting on a gas turbineengine as claimed in claim 1 wherein the annular body comprises aradially outer facing and a radially inner facing, the radially outerfacing and the radially inner facing defining a space therebetween. 10.A nacelle assembly adapted for mounting on a gas turbine engine asclaimed in claim 9 wherein the annular body comprises the outer facingand inner facing joining and extending rearward of the space to form asingle skin.
 11. A nacelle assembly adapted for mounting on a gasturbine engine as claimed in claim 9 wherein the outer facing and innerfacing are constructed from sandwich constructions.
 12. A nacelleassembly adapted for mounting on a gas turbine engine as claimed inclaim 9 wherein the space contains a lightweight core, the lightweightcore attached to both the outer facing and the inner facing.
 13. Anacelle assembly adapted for mounting on a gas turbine engine as claimedin claim 9 wherein the space contains a connector, the connectorattached to both the outer facing and the inner facing.
 14. A nacelleassembly adapted for mounting on a gas turbine engine as claimed inclaim 13 wherein the connector extends substantially in the axialdirection.
 15. A nacelle assembly adapted for mounting on a gas turbineengine as claimed in claim 13 wherein the connector extendssubstantially in the circumferential direction.
 16. A nacelle assemblyadapted for mounting on a gas turbine engine as claimed in claim 1wherein the annular body includes an access panel.
 17. A nacelleassembly adapted for mounting on a gas turbine engine as claimed inclaim 9 wherein the nacelle assembly comprises an engine accessory, theengine accessory is operationally located within the space in theannular body.